Pretreatment Study On The High Density And Difficultly Biodegradable Polyester Resin Wastewater

Due to the non-biodegradability of polyester resin wastewater , the high density polyester resin wastewater was pretreated by coagulation, Fe-C micro-electrolysis and Fenton reagent oxidation to reduce its toxicity to microorganisms, improve its biodegradability and decrease a portion of organic loading for subsequent biological treatment unit.During the polyester resin wastewater was pretreated by coagulation, the effect of flocculating agent and its dosage, coagulation-supporting agent and its dosage, initial pH value, water temperature, mixing time and clarifying time were investigated. The results showed that the optimal pretreatment process conditions of polyester resin wastewater by coagulation were using PAC flocculating agent and its dosage=500 mg/L, using PAM coagulation-supporting agent and its dosage=20 mg/L, initial pH of wastewater=8.0, water temperature=25℃, mixing time=20 min and clarifying time=1h. Under the optimal process conditions, the polyester resin wastewater COD_Cr removal rate could approach 29.82% after coagulation sedimentation, but the BOD₅/COD_Cr level of polyester resin wastewater only increased from 0.17 to 0.19, and its toxicity was not removed. It can not meet the subsequent biological treatment unit. So it was not feasible that polyester resin wastewater was preteated only by coagulation.As the polyester resin wastewater was pretreated by Fe-C micro-electrolysis, an orthogonal experimental method was adopted here. In the experiment, polyester resin wastewater was treated by Fe-C micro-electrolysis by changing the iron dosage, the ratio of iron to carbon (Fe/C, w/w) and initial pH of wastewater. Then based on the orthogonal experiment, single factor method was used to find out the best parameters of Fe-C micro-electrolysis. The result showed that in the orthogonal experimental factor levels, the original pH of wastewater ranked first, followed by the iron dosage and the ratio of iron to carbon. The optimal pretreatment process conditions of polyester resin wastewater by Fe-C micro-electrolysis were room temperature, initial pH=2.0, iron dosage=100 g/L, Fe/C =1/1(w/w), aeration reaction time=2h. Under the optimal process conditions, the biodegradable of polyester resin wastewater was improved observably through Fe-C micro-electrolysis treatment, its BOD₅/COD_Cr level increased from 0.17 to 0.33. In addition, the polyester resin wastewater COD_Cr removal efficiency could approach 50.91% after Fe-C micro-electrolysis treatment, so the organic loading of subsequent biological treatment unit could be decreased sharply.As the polyester resin wastewater was pretreated by Fenton reagent, an orthogonal experimental method was adopted here. In the experiment, polyester resin wastewater was oxidized by Fenton reagent by changing the dosage of H₂O₂, the dosage of Fe²⁺ and the original pH of wastewater. Then based on the orthogonal experiment, single factor method was used to find out the best parameters of Fenton reagent. The result showed that in the orthogonal experimental factor levels, the dosage of H₂O₂ ranked first, followed by the original pH of wastewater and dosage of Fe²⁺. The optimal pretreatment process conditions of polyester resin wastewater by Fenton reagent were room temperature, initial pH=2.9, H₂O₂/COD_Cr=2, [Fe²⁺]/[H₂O₂]=0.1, H₂O₂ and Fe²⁺ added by 4 times, reaction time=2 h. Under the optimal process conditions, the total COD_Cr removal rate of polyester resin wastewater was 76.45%. The biodegradability of polyester resin wastewater was improved remarkably after Fenton reagent treatment, its BOD₅/COD_Cr level increased from 0.17 to 0.33, the mean stoichiometry of Fenton reagent oxidation reaction was 0.382mgCOD_Cr/mg H₂O₂, and the effective using efficiency of H₂O₂ was 81.2%.On the base of general analysis of the technology and the cost through it, the pretreatment of Fe-C micro-electrolys is more practical in application. Meanwhile, the pretreatment of Fenton reagent had good effects, but it is more appropriate as a subsequent traetment due to its higher cost in the experiments.